Do fish sleep most of the night?? How often do they need to come up for air?

They don't sleep like you or I do. They keep a level of awareness for predators. But they do have a circadian (day/night) rhythm that needs a period of near total darkness for 6 plus hours. They also snooze, as it were, during the day.

The longest I've timed mine going without breathing was around 15 minutes, and that was a long time. Five minutes seems about average; frequently less. Watch and see. Report back. ;-}